ZnO layer was epitaxially grown with a high growth rate around 800nm/hour on C-sapphire at relatively low temperature 400°C by plasma-assisted epitaxy in oxygen plasma which was excited by radio- frequency power at 13.56MHz. Photoluminescence spectra, which were dominated by strong donor-bound exciton emissions and free-exciton emissions at 10K, indicated deep levels native-defects were well prevented in the layers grown by the optimized growth condition including the power to discharge oxygen gas. Initial layers grown at very low temperature increased the probability of ZnO-crystal nucleation, compared with the direct growth on the sapphire, and were very effective in decreasing surface roughness and then improving the crystal quality of the successively grown ZnO layers. The full-width at half-maximum of donor-bound exciton emission was dependent on the initial layer growth condition and the narrowest value of the FWHM was obtained as 1.7meV on PAE-layers deposited at 400°C on the initial layer grown at 150°C.